Sine rule

The sine rule states that if \(a\), \(b\) and \(c\) are the lengths of the sides of a triangle, and \(A\), \(B\) and \(C\) are the angles in the triangle; with \(A\) opposite \(a\), etc., then \[\frac{a}{\sin A} =
\frac{b}{\sin B} =
\frac{c}{\sin C}.\] This ratio is also equal to \(2R\), where \(R\) is the radius of the circumcircle of \(ABC\). Some regard this further equality as part of the sine rule.